1. Field of the Invention
The present invention relates to an ink jet print head, and in particular, to an ink jet print head in which a print element configured to generate thermal energy required to eject ink and a driving circuit configured to drive the print element s are formed on the same board.
The present invention is applicable not only to general print apparatuses but also apparatuses such as copiers, facsimile machines, and word processors as well as industrial print apparatuses combined with various processing apparatuses.
2. Description of the Related Art
An ink jet print apparatus is configured to print information on a print medium in response to a print signal by allowing a print head to eject ink through a plurality of fine nozzles. The ink jet print apparatus advantageously enables high-speed printing and offers high resolution and high image quality, while allowing a reduction in noise. The ink jet print apparatus is thus commonly used.
Some print heads used in ink jet print apparatuses are of an ink jet type configured to utilize thermal energy for printing. Such a print head allows print elements to be energized to heat ink to generate bubbles. Thus, pressure resulting from the generation of the bubbles is utilized to eject the ink through ejection ports for printing. Furthermore, the ink ejected through the ejection ports flies perpendicularly to the principal surface of a print element board. The ink thus impacts a print medium at a desired position. As a result, high-quality and high-grade printing is achieved.
However, if the ejection ports are inclined to the principal surface of the print element board or ink channels are shaped asymmetrically with respect to a corresponding pressure chamber, energy applied to the ink by the pressure resulting from the generation of bubbles is also asymmetric with respect to the pressure chamber. The asymmetry may cause the ejection direction of the ink to be inclined to the direction perpendicular to the principal surface of the print element board. Thus, the ink may impact the print medium at a position different from the desired one, thus lowering the print grade.
Thus, for the proper print grade, the ejection direction of the ink needs to be perpendicular to the principal surface of the print element board. In this case, the inclination of the ejection ports and the shape of the ink channels are important. Various methods have been proposed which are intended to reduce the inclination of the ejection direction of the ink to the direction perpendicular to the principal surface of the print element board.
Japanese Patent Laid-Open No. 2001-341309 describes that a print element in a recess portion is shaped rotationally symmetrically with respect to the center line of each ejection port, thus preventing ejected ink from flying in an inclined direction.
Furthermore, Japanese Patent Laid-Open No. 2008-162270 discloses a print head in which two channels are formed symmetrically with respect to each ejection port.
However, Japanese Patent Laid-Open Nos. 2001-341309 and 2008-162270 fail to refer to a phenomenon in which a step that may be formed on the bottom surface of the ink channel may disrupt the symmetry, causing the ejected ink to fly in an inclined direction. The present inventors have newly found that not only the symmetry of the channels but also a step of height several μm resulting from wires formed at the channel may affect the ejection direction.
A print element is provided in the pressure chamber and requires wires for energization. The wires connected to the print element normally include an individual wire and a common wire. Furthermore, to allow a reduction in wire installation area, the individual and common wires may be provided separately in the same layer, in a stack board, as that of the print element and in an underlying layer. When such a wiring layer is provided under the ink channel, a step structure is created on the inner bottom surface of the ink channel, that is, the surface of the board. If the step structure is present only in one of the ink channels arranged on the respective opposite sides of the pressure chamber, then the bottom surfaces of the ink channels are asymmetric with respect to the pressure chamber. The asymmetric structure of the ink channels may result in a difference in flow resistance between the ink channels. In this case, during ejection, pressure is generated in a biased manner. As a result, the ejected ink is inclined to the direction perpendicular to the principal surface of the print element board. Consequently, the ink may impact the print medium at an incorrect position or images may be unevenly formed.